JPS5823850B2 - Side chain chlorination method for aromatic compounds - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in the method of chlorinating the side chains of aromatic compounds having lower alkyl groups as side chains, such as toluene and xylene, using chlorine and under light irradiation. .

This type of chlorination reaction is usually carried out by introducing chlorine into a liquid phase reaction system in a glass reaction vessel while irradiating it with light.

However, in this case, the reaction liquid is often colored, which impairs light transmission, or deflagration occurs in the gas phase.

When the light transmittance deteriorates, the progress of side reactions takes priority, and nuclear chlorinated products and dehydrochlorinated condensates are generated as by-products, which reduces the purity and yield of the side chain chlorinated product, which is the desired product.

The main causes of the above-mentioned undesirable phenomena are:
It has been found that this is due to the presence of metal components such as iron as impurities in the reaction system, and therefore various techniques have been developed to reduce or eliminate the influence of impurity metal components as much as possible.

Conventional techniques effective for this purpose include adding substances such as urea, acid amide (US Pat. No. 2,695,873), and hexamethylenetetramine (US Pat. No. 2,817,632) that have the effect of capturing metal components to the reaction solution. A method in which chlorination is carried out in the presence of an N-lower alkyl substituted acid amide such as dimethylformamide (JP-A-48-76825) is known.

However, urea is poorly soluble or insoluble in the reaction solution,
This is not preferable because it adheres to the walls of the reaction vessel during the chlorination reaction and impedes the transmission of light.

On the other hand, hexamethylenetetramine, acid amide, dimethylformamide, etc. are soluble in the reaction solution, but even if purified products are used, particles that appear to be crystals are generated in the reaction solution during the chlorination reaction, and the reaction may be severe. The liquid becomes cloudy, which prevents light from passing into the reaction system.

The present invention was made for the purpose of providing a new and improved side chain chlorination method that eliminates the drawbacks of the conventional methods as described above, and effectively removes impurity metal components present in the reaction system. This is based on the discovery of a new metal component scavenger that captures metal components without adversely affecting the chlorination reaction.

That is, in the present invention, when photochlorinating the side chain of an aromatic compound having a lower alkyl group as a side chain, the reaction system has a general formula (wherein R1 and R2 are hydrogen or lower alkyl group n is 3
This is a method for side chain chlorination of aromatic compounds characterized by the presence of a lactam represented by

Aromatic compounds to be subjected to side chain chlorination according to the present invention include, for example, aromatic hydrocarbon compounds such as evaluene, xylene, and ethylbenzene, and furthermore, halogen groups in the nucleus or side chain of these aromatic compounds. Examples thereof include aromatic halogenated hydrocarbon compounds such as 0-chlorotoluene, p-chlorotoluene, and 0-dichloromethylbensitrifluoride.

The present invention can be carried out either in the presence or absence of a reaction solvent, but in the case of a compound that is liquid at room temperature, it can be used as a reaction solution as it is without particularly requiring a solvent.

In addition, in the case of compounds that are solid at room temperature, the reaction is usually carried out in the presence of a solvent, and the solvent is not particularly limited as long as it is inert to the chlorination reaction. A polychlorinated compound such as the like is used, and the volume is usually about 1 to 10 times that of the raw material.

Furthermore, according to the present invention, by-product impurities can be reduced by suppressing side reactions.

Thereby, it is also possible to use the reaction-finished liquid as it is as a starting material in the next reaction step without going through the step of recovering and purifying the target product from the obtained reaction-finished liquid.

As the lactam in the present invention, compounds represented by the above general formula can be used, such as those shown in Table 1 below.

In particular, ε~caprolactam is effective and easily available.

The amount of these lactams added can be changed as appropriate depending on the content of impurity metal components present in the reaction system and the type of lactam used, but it is usually 5 p of the weight of the reaction solution.
pm-10%, preferably 10 ppm to 5000 ppm
, more preferably 100 to 1000 ppm.

When carrying out the present invention, an aromatic compound to be side chain chlorinated and the above-mentioned lactam are placed in a transparent reaction vessel such as glass, and chlorine is introduced into the reaction vessel while irradiating light to chlorinate the side chain. Allow the chlorination reaction to proceed.

As chlorine, crude chlorine gas or dehydrated chlorine gas generated from an electrolytic tank, or liquid chlorine can be used.

As a light source, sunlight, discharge lamps, incandescent lamps, etc. can be used.
In particular, indium lamps, high-pressure mercury lamps, and ultra-high-pressure mercury lamps are industrially advantageous.

The temperature of the chlorination reaction may be any temperature at which the reaction solution can exist in a liquid state, but is preferably 60°C or higher.

The reaction time varies depending on the degree of chlorination, but is usually 10 minutes to 1
00 hours.

Dissolved chlorine, hydrogen chloride, etc. are expelled from the obtained reaction-completed liquid by a conventional method, and then the target product is recovered and purified by distillation and crystallization, if necessary.

Alternatively, as described above, the target product may be used as it is in the next reaction step without recovering and purifying the reaction solution.

As is clear from the above explanation, according to the present invention, even if impurity metal components exist in the reaction system, the influence of the impurity metal components can be prevented, and the phenomenon that prevents the transmission of light into the reaction system can be prevented by chlorine. Since it is possible to suppress the progress of side reactions and reduce the amount of byproducts, it is possible to obtain the desired product in high yield and purity.

The present invention will be further explained with reference to Examples below.

Examples 1 to 9 P-xylene 10 containing 10 ppm ferric chloride was placed in a glass reactor with an inner diameter of 5 CrrL and a height of 18 crrL.
6g and 50cm of the catalyst shown in Table 2 below were charged.

While maintaining the temperature of the reaction solution at 100 to 130°C, an indium lamp was irradiated from the side of the reactor with a light intensity of 150 W/m', and chlorine was introduced into the reaction solution at a rate of 1071/hour for 5 hours.

The reaction solution was only slightly colored, and remained transparent until the end of the reaction without precipitation or turbidity.

According to gas chromatographic analysis, the purity of the target product 1,4-bis(trichloromethyl)benzene was 97% by weight or more as shown in Table 2 in all cases.
The yield was 97% or more based on the theoretical value.

Note that no fouling of the reactor was observed in this reaction, and even if the reaction was repeated, there was no change in purity or yield.

Comparative Example 1 A reaction was carried out in the same manner as in Example 1 except that no catalyst was added, but the reaction solution turned reddish brown, the reaction did not proceed, and the target product was not obtained.

The results are shown in Table 2.

Comparative Example 2.4 When 50 m of the catalyst shown in Table 2 was charged and reacted in the same manner as in Example 1, sticky or crystalline impurities were produced and the reactor was contaminated.

The results are shown in Table 2.

Comparative Example 3.5 After completing the reaction of Comparative Example 2.4, a second reaction was repeated in the same manner as Comparative Example 2.4 using the same reactor.

As a result, the contamination of the reactor gradually increased and the reaction rate slowed down, so although the chlorine introduction time was extended by 5.5 to 7 hours, both the purity and yield of the target product decreased.

Claims (1)

[Scope of Claims] 1. When photochlorinating the side chain of an aromatic compound having a lower alkyl group as a side chain, the reaction system has a general formula (wherein R1 and R2 are hydrogen or a lower alkyl group, and n is 3 A method for side chain chlorination of aromatic compounds, characterized by the presence of a lactam represented by (representing an integer of ~7).